The present invention relates to a touch panel device for detecting the touch of an object, such as a finger and a pen, on the touch panel device, and more particularly relates to a touch panel device using IDTs (Inter Digital Transducers), for detecting the touched position by detecting attenuation and cutoff of surface acoustic wave (SAW).
With the spread of computer systems, mainly personal computers, there has been used a device for inputting new information or giving various instructions to a computer system by pointing at a position on a display screen of a display device on which information is displayed by the computer system, with a finger or a pen. In order to perform an input operation with respect to the information displayed on the display screen of the display device of a personal computer or the like by a touching method, it is necessary to detect a touched position (indicated position) on the display screen with high accuracy.
Well known examples of touch panel device for detecting a position touched by an object such as a finger and a pen are a device using a resistance film, and a device using ultrasonic waves. In the former device using a resistance film, a change in the resistance of the resistance film caused by the touch of the object on the resistance film is detected. This device has the advantage of low consumption of power, but has the problems in the aspects of the response time, detection performance and durability.
By contrast, in the device using ultrasonic waves, a position touched by the object is detected by propagating surface acoustic waves along a non-piezoelectric substrate, for example, and detecting attenuation of the surface acoustic waves caused by the touch of the object such as a finger and a pen on the non-piezoelectric substrate.
FIG. 1 is an illustration showing the structure of such a conventional touch panel device using surface acoustic waves (the first conventional example). A first surface acoustic wave oscillator 52a and a second surface acoustic wave oscillator 52b are provided at the upper left corner of a rectangular panel 51, a first surface acoustic wave receiver 53a is disposed at the lower left corner thereof, and a second surface acoustic wave receiver 53b is positioned at the upper right corner thereof. Moreover, reflectors 54a, 54b, 54c and 54d whose reflection surfaces are formed at an equal pitch are disposed at the four sides of the panel 51, that is, the upper side, lower side, left side and right side, respectively.
Here, a surface acoustic wave excited by the first surface acoustic wave oscillator 52a is reflected by the reflection surfaces of the reflector 54a, scanned and propagated on the panel 51 in a vertical direction (Y-axis direction), further reflected by the reflection surfaces of the reflector 54b, and then received by the first surface acoustic wave receiver 53a. Meanwhile, a surface acoustic wave excited by the second surface acoustic wave oscillator 52b is reflected by the reflection surfaces of the reflector 54c, scanned and propagated on the panel 51 in a lateral direction (X-axis direction), further reflected by the reflection surfaces of the reflector 54d, and then received by the second surface acoustic wave receiver 53b. FIG. 2 illustrates how such a surface acoustic wave is propagated.
In this example, since the surface acoustic waves enter each receiver after being reflected twice, they reach each receiver at intervals of ti=2D/Vs (D: the reflection surfaces formation pitch, Vs: the propagation speed of the surface acoustic waves). FIG. 3 shows a time-series reception signal obtained by each receiver at this time. When an object is touching the panel 51, since the level of the reception signal corresponding to that position is attenuated, it is possible to detect whether the panel 51 is touched by the object and the touched position by analyzing such a reception signal.
In order to increase the time resolution, i.e., in order to enable detection in a short time, a technique of shortening tR of FIG. 3 by increasing the propagation speed of the surface acoustic waves may be used; and in order to increase the spatial resolution, a technique of reducing the reflection surfaces formation pitch D may be employed. In order to detect the touched position with high precision, it is necessary to totally improve both of the time resolution and spatial resolution.
FIG. 4 shows a structural example of the first and second surface acoustic wave oscillators 52a and 52b. The surface acoustic wave is excited by applying a voltage through an electrode 56 to a wedge-shaped piezoelectric body 55 fabricated on the panel 51. Since the speed of this surface acoustic wave depends on the piezoelectric body 55, it is impossible to increase the speed. Moreover, in general, since the reflectors 54a, 54b, 54c and 54d are fabricated by cutting work, it is not easy to form the reflection surfaces at a very small pitch. It is thus difficult to improve the time resolution and spatial resolution and detect the touched position with high precision.
In contrast to such a touch panel device, the present inventors are carrying out research and development of a touch panel device that requires no reflector and uses IDTs, capable of being formed collectively using a photolithography technique, as transducers. In this touch panel device, elements, each composed of an IDT and a piezoelectric thin film, are used as an excitation element for exciting a surface acoustic wave and a receiving element for receiving a propagated surface acoustic wave.
FIG. 5 is an illustration showing the structure of such a conventional touch panel device using the IDTs (the second conventional example). In FIG. 5, numeral 61 represents a rectangular non-piezoelectric substrate, and a plurality of excitation elements 62, each composed of an input IDT and a piezoelectric thin film, for exciting surface acoustic waves are arranged into a line on one end of each of the X-direction and Y-direction of the non-piezoelectric substrate 61 so that the excitation elements 62 correspond to a plurality of tracks, respectively. Moreover, a plurality of receiving elements 63, each composed of an output IDT and a piezoelectric thin film, for receiving the surface acoustic waves are arranged into a line on the other end of each of the X-direction and Y-direction of the non-piezoelectric substrate 61 so that the receiving elements 63 face the excitation elements 62.
In the touch panel device shown in FIG. 5 (hereinafter referred to as the xe2x80x9cdiscrete-IDT type touch panel devicexe2x80x9d), a burst wave is applied to each excitation element 62 to excite the surface acoustic wave and propagate it along the non-piezoelectric substrate 61, and the propagated surface acoustic wave is received by each receiving element 63. Moreover, when an object touches the propagation path of the surface acoustic wave on the non-piezoelectric substrate 61, the surface acoustic wave is attenuated. Accordingly, it is possible to detect the presence or absence of the touch of the object and the touched position by detecting whether the reception signal level of the receiving elements 63 is attenuated or not.
In addition, the present inventors proposed a touch panel device (third conventional example) in which the excitation elements and the receiving elements are arranged so as to propagate surface acoustic waves in an oblique direction (diagonal direction) of the substrate. FIG. 6 is an illustration showing the structure of the IDTs of such a touch panel device (hereinafter referred to as the xe2x80x9cinclined continuous-IDT type touch panel devicexe2x80x9d). An excitation element 72 is disposed at one peripheral portion of a rectangular substrate 71. This excitation element 72 has an IDT 76 comprising facing electrode bases 74 and a plurality of comb-like electrode fingers 75 extended from the electrode bases 74 alternately. Besides, a receiving element 73 disposed at a peripheral section of the substrate 71 adjacent to the excitation element 72 has an IDT 76 having the same structure as that in the excitation element 72. In each IDT 76, the comb-like electrode fingers 75 are extended from the electrode bases 74 in a direction inclined from the facing direction of the electrode bases 74, i.e., in such a manner that the electrode fingers 75 are inclined from a direction perpendicular to the surfaces of the electrode bases 74. In such a touch panel device, since the apertures are gradually shifted, it is possible to detect a position touched by the object continuously (in an analog manner).
In the discrete-IDT type touch panel device shown in FIG. 5, the spatial resolution is determined by the installation interval of the IDTs, and it is easy to achieve a small installation interval of the IDTs. In other words, if the remaining time resolution can be improved, it is possible to realize highly precise detection of the touched position. On the other hand, in the inclined continuous-IDT type touch panel device shown in FIG. 6, since the IDT has a continuous structure, the spatial resolution is not limited. Therefore, in this example, it is also possible to realize highly precise detection of the touched position by improving the time resolution. Accordingly, the present inventors continue to carry out the research about a technique for improving the time resolution.
It is an object of the present invention to provide a touch panel device capable of improving the time resolution and realizing highly precise detection of a touched position.
Another object of the present invention is to provide a touch panel device capable of exciting a surface acoustic wave from an excitation element at an optimum frequency and achieving high gain reception.
Still another object of the present invention is to provide a touch panel device capable of preventing the influence of a reflected wave of a surface acoustic wave and accurately detecting a touched position.
Yet another object of the present invention is to provide a touch panel device capable of accurately detecting a touched position without receiving the influence of dirt and so on.
A touch panel device according to the first aspect is a touch panel device comprising at least one pair of excitation element for exciting a surface acoustic wave by application of a burst wave and receiving element for receiving the surface acoustic wave, on a substrate propagating the surface acoustic wave so that the excitation element and the receiving element face each other, each of the excitation element and the receiving element having an IDT composed of facing electrode bases and comb-like electrode fingers connected to the electrode bases, for detecting a position of an object touching the substrate by propagating the surface acoustic wave between the excitation element and the receiving element on the substrate and detecting the position based on a reception result at the receiving element, wherein a wave number of the burst wave to be applied to the excitation element is determined according to the number of the comb-like electrode fingers of the IDT of the excitation element.
A touch panel device according to the second aspect is a touch panel device comprising at least one pair of excitation element for exciting a surface acoustic wave by application of a burst wave and receiving element for receiving the surface acoustic wave, at peripheral sections in a diagonal direction of a rectangular substrate propagating the surface acoustic wave, each of the excitation element and the receiving element having an IDT composed of facing electrode bases and comb-like electrode fingers connected to the electrode bases, for detecting a position of an object touching the substrate by propagating the surface acoustic wave on the substrate in a diagonal direction between the excitation element and the receiving element and detecting the position based on a reception result at the receiving element, wherein the comb-like electrode fingers of the IDTs of the excitation element and the receiving element are connected to the electrode bases so that they are inclined from a facing direction of the electrode bases, and a wave number of the burst wave to be applied to the excitation element is determined according to an interval between the electrode bases of the IDT of the excitation element and an inclination angle and interval of the comb-like electrode fingers of the IDT of the excitation element.
A touch panel device according to the third aspect is a touch panel device comprising at least one pair of excitation element for exciting a surface acoustic wave by application of a burst wave and receiving element for receiving the surface acoustic wave, on a substrate propagating the surface acoustic wave so that the excitation element and the receiving element face each other, each of the excitation element and the receiving element having an IDT composed of facing electrode bases and comb-like electrode fingers connected to the electrode bases, for detecting a position of an object touching the substrate by propagating the surface acoustic wave between the excitation element and the receiving element on the substrate and detecting the position based on a reception result at the receiving element, wherein a wave number of the burst wave to be applied to the excitation element is determined according to a result of receiving the surface acoustic wave, which was excited by the application of the burst wave to the excitation element, at the receiving element.
The propagation speed of the surface acoustic wave is determined mainly by the type of a piezoelectric body, and the propagation time is determined by the size of the substrate. Accordingly, in order to improve the time resolution, i.e., in order to perform efficient detection within a short time, it is necessary to optimize the time taken for driving the IDT, i.e., the wave number of the burst wave, and therefore, in the first through third aspects, an optimum wave number of the burst wave is determined.
In the first aspect, noting the reception signal gain and the number of the comb-like electrode fingers of the IDT in a discrete-IDT type touch panel device, the wave number of the burst wave is determined according to the number of the comb-like electrode fingers of the IDT. The maximum gain of the reception signal is obtained by applying the same number of burst wave as the number of the comb-like electrode fingers, and, when a burst wave number equal to or more than the number of comb-like electrode fingers is applied, the reception signal gain is fixed. Therefore, by arranging the wave number of the applied burst wave to be equal to the number of the comb-like electrode fingers, the wave number of the burst wave is optimized, thereby achieving highly accurate detection and high time resolution.
Moreover, according to the second aspect, even if the touch panel device is of an inclined continuous-IDT type, the wave number of the burst wave is determined by considering the maximum reception signal gain, but, in this case, the wave number of the burst wave is determined according to the interval of the electrode bases and the inclination angle and interval of the comb-like electrode fingers of the IDT. It is therefore possible to obtain an optimum wave number of the burst wave and increase the time resolution.
Furthermore, according to the third aspect, for example, during activation of the device, the burst wave is applied to the excitation element to excite the surface acoustic wave, the excited surface acoustic wave is received by the receiving element, and the optimum wave number of the burst wave is determined according to the reception result. For instance, the wave number of the burst wave that causes the reception result to show the maximum value is determined as the optimum wave number. Accordingly, it is possible to obtain an optimum burst wave number according to the operating environment and operating condition, thereby increasing the time resolution.
A touch panel device according to the fourth aspect is based on any one of the first through third aspects, wherein a drive frequency of the IDT of the excitation element is determined according to results of receiving surface acoustic waves, which were excited at different frequencies by the excitation element, at the receiving element. According to the fourth aspect, for example, during activation of the device, the IDT is driven at different frequencies in the vicinity of the initially set frequency to excite the excitation element, the excited surface acoustic wave is received by the receiving element, and a frequency that causes the reception result to show the maximum value is determined as the optimum frequency. It is therefore possible to always achieve high gain reception even when the operating environment and operating condition change.
A touch panel device according to the fifth aspect is based on any one of the first through fourth aspects, wherein a time interval between sequential burst waves to be applied to the excitation element is not less than a reception time of the surface acoustic wave at the receiving element. It has been considered that the surface acoustic wave excited by the excitation element is reflected by the receiving element and the reflected wave enters the excitation element and viciously affects the detection accuracy. According to the fifth aspect, in order to reduce such influence of the reflected wave, the burst wave is applied to the excitation element so that the burst wave interval is not less than the reception time of the surface acoustic wave at the receiving element.
A touch panel device according to the sixth aspect is based on any one of the first through fifth aspects, wherein a reception signal obtained by the receiving element is binarized based on a predetermined threshold, and the position of the object is detected based on the binarization result. According to the sixth aspect, the reception signal obtained by the receiving element is binarized based on the predetermined threshold, and the position of the object is detected based on the binarization result. It is therefore possible to detect the touched position by simple processes.
A touch panel device according to the seventh aspect is based on the sixth aspect, wherein the position of the object is detected based on a first timing representing a transition from rise to fall of a binarized signal obtained by binarizing the reception signal obtained by the receiving element based on the predetermined threshold, and the width of the object is detected based on the first timing and a second timing representing a transition from fall to rise of the binarized signal. According to the seventh aspect, the first timing representing a transition from rise to fall in the binarization result of the reception signal based on the threshold and the second timing representing a transition from fall to rise are detected, the touched position is obtained by multiplying the time of the first timing by the speed of the surface acoustic wave, and the width of the object is obtained by multiplying the time difference between the first and second timings by the speed of the surface acoustic wave. It is therefore possible to simply detect the touched position and width of the object.
A touch panel device according to the eighth aspect is based on the sixth or seventh aspect, wherein a plurality of sampling points are extracted for the reception signal obtained by the receiving element, and the threshold for use in the binarization is set individually for each of the plurality of sampling points. According to the eighth aspect, the threshold for use in the binarization is set individually for each of the plurality of sampling points. For example, for a portion where the substrate itself is dirty and the surface acoustic wave is attenuated even when the object is not present, a lower threshold than in other portions is set. It is therefore possible to prevent erroneous detection due to dirt and perform accurate detection.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.